Medical Device Daily National Editor

Stroke damage causing partial paralysis – that is, to one side of the body – is a tricky thing. The conventional model here is that when paralysis is on the left side of the body, there is stroke damage to the right side of the brain; right-side paralysis, left-side stroke damage to the brain.

Brain-computer interfaces (BCIs) have been used based on this same model. These devices are used to pick up signals from the brain which are then used to guide motorized prosthetics restoring movement to paralyzed limbs resulting from spinal chord injury – right-brain sensing assisting left-side activity, and vice versa.

Based on the opposite-side model, it was thought that BCIs can't be used for partially paralyzed stroke patients, given the loss of opposite-side signals.

Enter a new model for brain activity: one showing that same-side brain signals are involved in movement.

Eric Leuthardt, MD, assistant professor of biomedical engineering at Washington University School of Medicine and a physician at Barnes-Jewish Hospital (both St. Louis), explains that "we've come to realize that there's actually some ipsilateral, or same-sided control signals, involved in movement." This, he told Medical Device Daily, offers the hope that BCIs can be used to aid partial-paralysis stroke patients.

"Now we've shown these signals can be detected and are separable from signals that control the opposite side of the body ... [W]e may be able to use a BCI to restore function." The technique, Leuthardt told MDD, involves placing a "grid" of electrodes over the brain to pick up these same-side signals.

"It's relatively simple," he said. The grid consists of "an elastic, clear plastic embedded with 64 electrodes in a common configuration." This grid is then attached to recording equipment by wires "tunneled through the scalp."

BCIs formerly consisted of small electrodes implanted inside brain tissue to record activity from individual brain cells. The new approach developed by Leuthardt and colleagues – termed electrocorticography (EcoG) – records signals from many neurons all at once. And Leuthardt's team has shown that the ECoG method provides insights into what a patient wants to do, such as a desire to move a hand or to speak, by analyzing these multiple signals from groups of neurons, rather than single neurons. Examples include a desire to speak or move the hand and pick up something.

"The old approach was good for acquiring significant signal control, but it suffered from the problem of scar encapsulation," Leuthardt explains. "When the electrodes are in the brain for three to six months, scars will form around them that prohibit them from recording brain signals."

In any future clinical uses, the grid placed on the brain would be made permanent, its signals sent to a monitor wirelessly. Likely patient candidates would be identified, he said, using standard methods, such as clinical examination and MRI.

The study using ECoG was carried out with six epilepsy patients to identify brain areas where seizures originated for possible surgical removal, temporarily implanting the grids over their brains. The researchers asked the patients to perform tasks with their hands, and they found that the grids picked up ipsilateral brain signals during the tasks.

The study enrolled epilepsy patients, he said, because the technique of measuring their brains signals is "a standard of care – it's already being done.

"This is one of those rare times when we can actually look at brain activity in humans," he said. "You have to have a normal functioning brain [providing movement to both sides] to see if we can apply these methods to help in a situation where we have only half the function of your brain."

"We were able to identify distinct anatomic locations in the brain where these ipsilateral hand control signals occur and to show that they typically are found in the lower-frequency regions of the spectrum of brain activity detected by the BCI," Leuthardt said. "Three of our patients could use these signals or opposite-sided hand control signals to move a computer cursor on a screen."

Leuthardt said that the basic strategy being pursued is to superimpose the team's new discoveries on previous research he has led, reported in 2005, that a patient implanted with a BCI could use the implant to control a video game.

"This allows us to piggy back research on what's already being done on patients."

Real-life clinical uses of these techniques are in the future, of course, and will involve a combination of technologies.

Methods for looking at brain function to produce "brain mapping," he said, may be an 8, with a 10 representing full development.

He said that his team's research on brain/computer interfacing is "likely a 5 or a 6 – we're getting closer, realistically, to clinical trials."

And the use of EcoG in the particular paralysis research "is probably a 4."

The study was published Oct. 16 in the online issue of Stroke.

Funding from the James S. McDonnell Foundation provided support for this research. Any future product commercialization, he said, will be pushed by Washington University, which owns the patents to the technology being developed.